Method for transmitting sidelink data in a d2d communication system and device therefor

ABSTRACT

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for transmitting a sidelink data in a D2D communication system, the method comprising: configuring to communicate with at least one destination; receiving a sidelink data corresponding to a destination of the at least one destination from an eNB; receiving a sidelink grant MAC CE including at least one sidelink grant and at least one destination identifier associated with a corresponding sidelink grant from the eNB; and transmitting the sidelink data to the destination by using a sidelink grant associated with the destination in the sidelink grant MAC CE if there is the sidelink grant associated with the destination in the sidelink grant MAC CE.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for transmitting a sidelink data in a D2D(Device to Device) communication system and a device therefor.

BACKGROUND ART

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, referred to as LTE) communication system isdescribed in brief.

FIG. 1 is a view schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system. An Evolved UniversalMobile Telecommunications System (E-UMTS) is an advanced version of aconventional Universal Mobile Telecommunications System (UMTS) and basicstandardization thereof is currently underway in the 3GPP. E-UMTS may begenerally referred to as a Long Term Evolution (LTE) system. For detailsof the technical specifications of the UMTS and E-UMTS, reference can bemade to Release 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs(eNBs), and an Access Gateway (AG) which is located at an end of thenetwork (E-UTRAN) and connected to an external network. The eNBs maysimultaneously transmit multiple data streams for a broadcast service, amulticast service, and/or a unicast service.

One or more cells may exist per eNB. The cell is set to operate in oneof bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides adownlink (DL) or uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be set to provide differentbandwidths. The eNB controls data transmission or reception to and froma plurality of UEs. The eNB transmits DL scheduling information of DLdata to a corresponding UE so as to inform the UE of a time/frequencydomain in which the DL data is supposed to be transmitted, coding, adata size, and hybrid automatic repeat and request (HARQ)-relatedinformation. In addition, the eNB transmits UL scheduling information ofUL data to a corresponding UE so as to inform the UE of a time/frequencydomain which may be used by the UE, coding, a data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic may be used between eNBs. A core network (CN) mayinclude the AG and a network node or the like for user registration ofUEs. The AG manages the mobility of a UE on a tracking area (TA) basis.One TA includes a plurality of cells.

Device to device (D2D) communication refers to the distributedcommunication technology that directly transfers traffic betweenadjacent nodes without using infrastructure such as a base station. In aD2D communication environment, each node such as a portable terminaldiscovers user equipment physically adjacent thereto and transmitstraffic after setting communication session. In this way, since D2Dcommunication may solve traffic overload by distributing trafficconcentrated into the base station, the D2D communication may havereceived attention as the element technology of the next generationmobile communication technology after 4G. For this reason, the standardinstitute such as 3GPP or IEEE has proceeded to establish the D2Dcommunication standard on the basis of LTE-A or Wi-Fi, and Qualcomm hasdeveloped their own D2D communication technology.

It is expected that the D2D communication contributes to increasethroughput of a mobile communication system and create new communicationservices. Also, the D2D communication may support proximity based socialnetwork services or network game services. The problem of link of a userequipment located at a shade zone may be solved by using a D2D link as arelay. In this way, it is expected that the D2D technology will providenew services in various fields.

The D2D communication technologies such as infrared communication,ZigBee, radio frequency identification (RFID) and near fieldcommunications (NFC) based on the RFID have been already used. However,since these technologies support communication only of a specific objectwithin a limited distance (about 1 m), it is difficult for thetechnologies to be regarded as the D2D communication technologiesstrictly.

Although the D2D communication has been described as above, details of amethod for transmitting data from a plurality of D2D user equipmentswith the same resource have not been suggested.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method and device for a method for transmitting a sidelink data in aD2D communication system. The technical problems solved by the presentinvention are not limited to the above technical problems and thoseskilled in the art may understand other technical problems from thefollowing description.

Technical Solution

The object of the present invention can be achieved by providing amethod for User Equipment (UE) operating in a wireless communicationsystem as set forth in the appended claims.

In another aspect of the present invention, provided herein is acommunication apparatus as set forth in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

Advantageous Effects

It is invented that a Relay UE receives at least one SL grant via MACsignal from an eNB, wherein each SL grant is to be used for SL datatransmission of one ProSe destination.

It will be appreciated by persons skilled in the art that that theeffects achieved by the present invention are not limited to what hasbeen particularly described hereinabove and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram showing a network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as an example of a wirelesscommunication system;

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS), and FIG. 2B is ablock diagram depicting architecture of a typical E-UTRAN and a typicalEPC;

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3rd generationpartnership project (3GPP) radio access network standard;

FIG. 4 is a diagram of an example physical channel structure used in anE-UMTS system;

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention

FIG. 6 is an example of default data path for a normal communication;

FIGS. 7 and 8 are examples of data path scenarios for a proximitycommunication;

FIG. 9 is a conceptual diagram illustrating for a Layer 2 Structure forSidelink;

FIG. 10A is a conceptual diagram illustrating for User-Plane protocolstack for ProSe Direct Communication, and FIG. 10B is Control-Planeprotocol stack for ProSe Direct Communication;

FIG. 11 is an example for PC5 interface between remote UEs and a relayUE; and FIG. 12 is a diagram for transmitting a sidelink data in a D2Dcommunication system according to embodiments of the present invention;

FIGS. 13A and 13B are examples for the SL grant MAC CE according toembodiments of the present invention; and

FIG. 14 is an example for transmitting a sidelink data in a D2Dcommunication system according to embodiments of the present invention.

BEST MODE

Universal mobile telecommunications system (UMTS) is a 3rd Generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3G LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

Hereinafter, structures, operations, and other features of the presentinvention will be readily understood from the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Embodiments described later are examples in which technicalfeatures of the present invention are applied to a 3GPP system.

Although the embodiments of the present invention are described using along term evolution (LTE) system and a LTE-advanced (LTE-A) system inthe present specification, they are purely exemplary. Therefore, theembodiments of the present invention are applicable to any othercommunication system corresponding to the above definition. In addition,although the embodiments of the present invention are described based ona frequency division duplex (FDD) scheme in the present specification,the embodiments of the present invention may be easily modified andapplied to a half-duplex FDD (H-FDD) scheme or a time division duplex(TDD) scheme.

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS). The E-UMTS may bealso referred to as an LTE system. The communication network is widelydeployed to provide a variety of communication services such as voice(VoIP) through IMS and packet data.

As illustrated in FIG. 2A, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNodeB) 20, and a plurality of user equipment (UE) 10 maybe located in one cell. One or more E-UTRAN mobility management entity(MME)/system architecture evolution (SAE) gateways 30 may be positionedat the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNodeB 20 to UE10, and “uplink” refers to communication from the UE to an eNodeB. UE 10refers to communication equipment carried by a user and may be alsoreferred to as a mobile station (MS), a user terminal (UT), a subscriberstation (SS) or a wireless device.

FIG. 2B is a block diagram depicting architecture of a typical E-UTRANand a typical EPC.

As illustrated in FIG. 2B, an eNodeB 20 provides end points of a userplane and a control plane to the UE 10. MME/SAE gateway 30 provides anend point of a session and mobility management function for UE 10. TheeNodeB and MME/SAE gateway may be connected via an Si interface.

The eNodeB 20 is generally a fixed station that communicates with a UE10, and may also be referred to as a base station (BS) or an accesspoint. One eNodeB 20 may be deployed per cell. An interface fortransmitting user traffic or control traffic may be used between eNodeBs20.

The MME provides various functions including NAS signaling to eNodeBs20, NAS signaling security, AS Security control, Inter CN node signalingfor mobility between 3GPP access networks, Idle mode UE Reachability(including control and execution of paging retransmission), TrackingArea list management (for UE in idle and active mode), PDN GW andServing GW selection, MME selection for handovers with MME change, SGSNselection for handovers to 2G or 3G 3GPP access networks, Roaming,Authentication, Bearer management functions including dedicated bearerestablishment, Support for PWS (which includes ETWS and CMAS) messagetransmission. The SAE gateway host provides assorted functions includingPer-user based packet filtering (by e.g. deep packet inspection), LawfulInterception, UE IP address allocation, Transport level packet markingin the downlink, UL and DL service level charging, gating and rateenforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAEgateway 30 will be referred to herein simply as a “gateway,” but it isunderstood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNodeB 20 and gateway 30via the Si interface. The eNodeBs 20 may be connected to each other viaan X2 interface and neighboring eNodeBs may have a meshed networkstructure that has the X2 interface.

As illustrated, eNodeB 20 may perform functions of selection for gateway30, routing toward the gateway during a Radio Resource Control (RRC)activation, scheduling and transmitting of paging messages, schedulingand transmitting of Broadcast Channel (BCCH) information, dynamicallocation of resources to UEs 10 in both uplink and downlink,configuration and provisioning of eNodeB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE-IDLE state management,ciphering of the user plane, System Architecture Evolution (SAE) bearercontrol, and ciphering and integrity protection of Non-Access Stratum(NAS) signaling.

The EPC includes a mobility management entity (MME), a serving-gateway(S-GW), and a packet data network-gateway (PDN-GW). The MME hasinformation about connections and capabilities of UEs, mainly for use inmanaging the mobility of the UEs. The S-GW is a gateway having theE-UTRAN as an end point, and the PDN-GW is a gateway having a packetdata network (PDN) as an end point.

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3GPP radioaccess network standard. The control plane refers to a path used fortransmitting control messages used for managing a call between the UEand the E-UTRAN. The user plane refers to a path used for transmittingdata generated in an application layer, e.g., voice data or Internetpacket data.

A physical (PHY) layer of a first layer provides an information transferservice to a higher layer using a physical channel. The PHY layer isconnected to a medium access control (MAC) layer located on the higherlayer via a transport channel. Data is transported between the MAC layerand the PHY layer via the transport channel Data is transported betweena physical layer of a transmitting side and a physical layer of areceiving side via physical channels. The physical channels use time andfrequency as radio resources. In detail, the physical channel ismodulated using an orthogonal frequency division multiple access (OFDMA)scheme in downlink and is modulated using a single carrier frequencydivision multiple access (SC-FDMA) scheme in uplink.

The MAC layer of a second layer provides a service to a radio linkcontrol (RLC) layer of a higher layer via a logical channel. The RLClayer of the second layer supports reliable data transmission. Afunction of the RLC layer may be implemented by a functional block ofthe MAC layer. A packet data convergence protocol (PDCP) layer of thesecond layer performs a header compression function to reduceunnecessary control information for efficient transmission of anInternet protocol (IP) packet such as an IP version 4 (IPv4) packet oran IP version 6 (IPv6) packet in a radio interface having a relativelysmall bandwidth.

A radio resource control (RRC) layer located at the bottom of a thirdlayer is defined only in the control plane. The RRC layer controlslogical channels, transport channels, and physical channels in relationto configuration, re-configuration, and release of radio bearers (RBs).An RB refers to a service that the second layer provides for datatransmission between the UE and the E-UTRAN. To this end, the RRC layerof the UE and the RRC layer of the E-UTRAN exchange RRC messages witheach other.

One cell of the eNB is set to operate in one of bandwidths such as 1.25,2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to a plurality of UEs in the bandwidth. Differentcells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the E-UTRAN tothe UE include a broadcast channel (BCH) for transmission of systeminformation, a paging channel (PCH) for transmission of paging messages,and a downlink shared channel (SCH) for transmission of user traffic orcontrol messages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted through the downlink SCH and mayalso be transmitted through a separate downlink multicast channel (MCH).

Uplink transport channels for transmission of data from the UE to theE-UTRAN include a random access channel (RACH) for transmission ofinitial control messages and an uplink SCH for transmission of usertraffic or control messages. Logical channels that are defined above thetransport channels and mapped to the transport channels include abroadcast control channel (BCCH), a paging control channel (PCCH), acommon control channel (CCCH), a multicast control channel (MCCH), and amulticast traffic channel (MTCH).

FIG. 4 is a view showing an example of a physical channel structure usedin an E-UMTS system. A physical channel includes several subframes on atime axis and several subcarriers on a frequency axis. Here, onesubframe includes a plurality of symbols on the time axis. One subframeincludes a plurality of resource blocks and one resource block includesa plurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use certain subcarriers of certain symbols (e.g., a firstsymbol) of a subframe for a physical downlink control channel (PDCCH),that is, an L1/L2 control channel. In FIG. 4, an L1/L2 controlinformation transmission area (PDCCH) and a data area (PDSCH) are shown.In one embodiment, a radio frame of 10 ms is used and one radio frameincludes 10 subframes. In addition, one subframe includes twoconsecutive slots. The length of one slot may be 0.5 ms. In addition,one subframe includes a plurality of OFDM symbols and a portion (e.g., afirst symbol) of the plurality of OFDM symbols may be used fortransmitting the L1/L2 control information. A transmission time interval(TTI) which is a unit time for transmitting data is 1 ms.

A base station and a UE mostly transmit/receive data via a PDSCH, whichis a physical channel, using a DL-SCH which is a transmission channel,except a certain control signal or certain service data. Informationindicating to which UE (one or a plurality of UEs) PDSCH data istransmitted and how the UE receive and decode PDSCH data is transmittedin a state of being included in the PDCCH.

For example, in one embodiment, a certain PDCCH is CRC-masked with aradio network temporary identity (RNTI) “A” and information about datais transmitted using a radio resource “B” (e.g., a frequency location)and transmission format information “C” (e.g., a transmission blocksize, modulation, coding information or the like) via a certainsubframe. Then, one or more UEs located in a cell monitor the PDCCHusing its RNTI information. And, a specific UE with RNTI “A” reads thePDCCH and then receive the PDSCH indicated by B and C in the PDCCHinformation.

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention.

The apparatus shown in FIG. 5 can be a user equipment (UE) and/or eNBadapted to perform the above mechanism, but it can be any apparatus forperforming the same operation.

As shown in FIG. 5, the apparatus may comprises a DSP/microprocessor(110) and RF module (transmiceiver; 135). The DSP/microprocessor (110)is electrically connected with the transciver (135) and controls it. Theapparatus may further include power management module (105), battery(155), display (115), keypad (120), SIM card (125), memory device (130),speaker (145) and input device (150), based on its implementation anddesigner's choice.

Specifically, FIG. 5 may represent a UE comprising a receiver (135)configured to receive a request message from a network, and atransmitter (135) configured to transmit the transmission or receptiontiming information to the network. These receiver and the transmittercan constitute the transceiver (135). The UE further comprises aprocessor (110) connected to the transceiver (135: receiver andtransmitter).

Also, FIG. 5 may represent a network apparatus comprising a transmitter(135) configured to transmit a request message to a UE and a receiver(135) configured to receive the transmission or reception timinginformation from the UE. These transmitter and receiver may constitutethe transceiver (135). The network further comprises a processor (110)connected to the transmitter and the receiver. This processor (110) maybe configured to calculate latency based on the transmission orreception timing information.

Recently, Proximity-based Service (ProSe) has been discussed in 3GPP.The ProSe enables different UEs to be connected (directly) each other(after appropriate procedure(s), such as authentication), through eNBonly (but not further through Serving Gateway (SGW)/Packet Data NetworkGateway (PDN-GW, PGW)), or through SGW/PGW. Thus, using the ProSe,device to device direct communication can be provided, and it isexpected that every devices will be connected with ubiquitousconnectivity. Direct communication between devices in a near distancecan lessen the load of network. Recently, proximity-based social networkservices have come to public attention, and new kinds of proximity-basedapplications can be emerged and may create new business market andrevenue. For the first step, public safety and critical communicationare required in the market. Group communication is also one of keycomponents in the public safety system. Required functionalities are:Discovery based on proximity, Direct path communication, and Managementof group communications.

Use cases and scenarios are for example: i) Commercial/social use, ii)Network offloading, iii) Public Safety, iv) Integration of currentinfrastructure services, to assure the consistency of the userexperience including reachability and mobility aspects, and v) PublicSafety, in case of absence of EUTRAN coverage (subject to regionalregulation and operator policy, and limited to specific public-safetydesignated frequency bands and terminals)

FIG. 6 is an example of default data path for communication between twoUEs. With reference to FIG. 6, even when two UEs (e.g., UE1, UE2) inclose proximity communicate with each other, their data path (userplane) goes via the operator network. Thus a typical data path for thecommunication involves eNB(s) and/or Gateway(s) (GW(s)) (e.g., SGW/PGW).

FIGS. 7 and 8 are examples of data path scenarios for a proximitycommunication. If wireless devices (e.g., UE1, UE2) are in proximity ofeach other, they may be able to use a direct mode data path (FIG. 7) ora locally routed data path (FIG. 8). In the direct mode data path,wireless devices are connected directly each other (after appropriateprocedure(s), such as authentication), without eNB and SGW/PGW. In thelocally routed data path, wireless devices are connected each otherthrough eNB only.

FIG. 9 is a conceptual diagram illustrating for a Layer 2 structure forSidelink. Sidelink communication is a mode of communication whereby UEscan communicate with each other directly over the PC5 interface. Thiscommunication mode is supported when the UE is served by E-UTRAN andwhen the UE is outside of E-UTRA coverage. Only those UEs authorized tobe used for public safety operation can perform sidelink communication.

In order to perform synchronization for out of coverage operation UE(s)may act as a synchronization source by transmitting SBCCH and asynchronization signal. SBCCH carries the most essential systeminformation needed to receive other sidelink channels and signals. SBCCHalong with a synchronization signal is transmitted with a fixedperiodicity of 40 ms. When the UE is in network coverage, the contentsof SBCCH are derived from the parameters signalled by the eNB. When theUE is out of coverage, if the UE selects another UE as a synchronizationreference, then the content of SBCCH is derived from the received SBCCH;otherwise UE uses pre-configured parameters. SIB18 provides the resourceinformation for synchronization signal and SBCCH transmission. There aretwo pre-configured subframes every 40 ms for out of coverage operation.UE receives synchronization signal and SBCCH in one subframe andtransmit synchronization signal and SBCCH on another subframe if UEbecomes synchronization source based on defined criterion.

UE performs sidelink communication on subframes defined over theduration of Sidelink Control period. The Sidelink Control period is theperiod over which resources allocated in a cell for sidelink controlinformation and sidelink data transmissions occur. Within the SidelinkControl period the UE sends sidelink control information followed bysidelink data. Sidelink control information indicates a Layer 1 ID andcharacteristics of the transmissions (e.g. MCS, location of theresource(s) over the duration of Sidelink Control period, timingalignment).

The UE performs transmission and reception over Uu and PC5 with thefollowing decreasing priority order:

-   -   Uu transmission/reception (highest priority);    -   PC5 sidelink communication transmission/reception;    -   PC5 sidelink discovery announcement/monitoring (lowest        priority).

FIG. 10A is a conceptual diagram illustrating for User-Plane protocolstack for ProSe Direct Communication, and FIG. 10B is Control-Planeprotocol stack for ProSe Direct Communication.

FIG. 10A shows the protocol stack for the user plane, where PDCP, RLCand MAC sublayers (terminate at the other UE) perform the functionslisted for the user plane (e.g. header compression, HARQretransmissions). The PC5 interface consists of PDCP, RLC, MAC and PHYas shown in FIG. 10A.

User plane details of ProSe Direct Communication: i) there is no HARQfeedback for sidelink communication, ii) RLC UM is used for sidelinkcommunication, iii) RLC UM is used for sidelink communication, iv) areceiving RLC UM entity used for sidelink communication does not need tobe configured prior to reception of the first RLC UMD PDU, and v) ROHCUnidirectional Mode is used for header compression in PDCP for sidelinkcommunication.

A UE may establish multiple logical channels. LCID included within theMAC subheader uniquely identifies a logical channel within the scope ofone Source Layer-2 ID and ProSe Layer-2 Group ID combination. Parametersfor logical channel prioritization are not configured. The Accessstratum (AS) is provided with the PPPP of protocol data unit transmittedover PC5 interface by higher layer. There is a PPPP associated with eachlogical channel.

SL-RNTI is an unique identification used for ProSe Direct CommunicationScheduling.

The Source Layer-2 ID identifies the sender of the data in sidelinkcommunication. The Source Layer-2 ID is 24 bits long and is usedtogether with Destination Layer-2 ID and LCID for identification of theRLC UM entity and PDCP entity in the receiver.

The destination Layer-2 ID identifies the target of the data in sidelinkcommunication. The Destination Layer-2 ID is 24 bits long and is splitin the MAC layer into two bit strings: i) One bit string is the LSB part(8 bits) of Destination Layer-2 ID and forwarded to physical layer asGroup Destination ID. This identifies the target of the intended data insidelink control information and is used for filtering of packets at thephysical layer. And ii) Second bit string is the MSB part (16 bits) ofthe Destination Layer-2 ID and is carried within the MAC header. This isused for filtering of packets at the MAC layer.

No Access Stratum signalling is required for group formation and toconfigure Source Layer-2 ID, Destination Layer-2 ID and GroupDestination ID in the UE. These identities are either provided by higherlayer or derived from identities provided by higher layer. In case ofgroupcast and broadcast, the ProSe UE ID provided by higher layer isused directly as the Source Layer-2 ID and the ProSe Layer-2 Group IDprovided by higher layer is used directly as the Destination Layer-2 IDin the MAC layer. In case of one-to-one communications, higher layerprovides Source Layer-2 ID and Destination Layer-2 ID.

FIG. 10B shows the protocol stack for the control plane.

A UE does not establish and maintain a logical connection to receivingUEs prior to one-to-many a sidelink communication. Higher layerestablish and maintain a logical connection for one-to-one sidelinkcommunication including ProSe UE-to-Network Relay operation.

The Access Stratum protocol stack for SBCCH in the PC5 interfaceconsists of RRC, RLC, MAC and PHY as shown below in FIG. 10B.

The PPPP is a ProSe Per-Packet Priority. The ProSe Per-Packet Priorityis summarized as follows:

i) a single UE shall be able to transmit packets of different prioritieson PC5, ii) the UE upper layers provide to the access stratum a ProSePer Packet Priority from a range of possible values, iii) the ProSe PerPacket Priority is used to support preferential transmission of packetsboth intra-UE and across different UEs, iv) the support of 8 prioritylevels for the ProSe Per Packet Priority should be sufficient, v) theProSe Per Packet Priority applies to all PC5 traffic, and vi) the ProSePer Packet Priority is independent of the layer-2 destination of thetransmission.

From the above summary, it seems that SA2 think ProSe packetprioritization based on PPP is very important and should be supported inPC5 interface in any case. Keeping this observation in mind, we explainhow the LCP procedures should be changed from Rel-12.

FIG. 11 is an example for PC5 interface between remote UEs and a relayUE.

In ProSe, a UE communicates with other UEs directly over PC5 interface.

By introducing a Relay UE for UE-to-NW relay, a remote UE transmits datato an eNB via the Relay UE, and the eNB transmits data to the remote UEvia the Relay UE. I.e., the Relay UE relays data to/from eNB.

As data transfer between the remote UE and the Relay UE is ProSecommunication, the Relay UE is communicating with the remote UE over PC5interface. In the meantime, as data transfer between the Relay UE andthe eNB is a normal uplink/downlink (Uu) communication, the Relay UE iscommunicating with the eNB over Uu interface. This implies that if datahas higher priority in PC5 communication, it should also be higherprioritized in Uu communication.

Over PC5 interface, Per-Packet Priority (PPP), is used to prioritize acertain packet, where the priority is independent with ProSe destinationor ProSe UE. In order to prioritize the packet with higher priority overUu interface as well, the Relay UE needs to know the priority of thepacket so that the Relay UE provides more opportunities of transmissionto the packet with higher priority.

In order to transmit on the SL-SCH, the MAC entity must have a sidelinkgrant. The sidelink grant is selected as follows: if the MAC entity isconfigured to receive a sidelink grant dynamically on the PDCCH and moredata is available in STCH than can be transmitted in the current SCperiod, the MAC entity shall determine a set of subframes in whichtransmission of SCI and transmission of first transport block occurusing the received sidelink grant, consider the received sidelink grantto be a configured sidelink grant occurring in those subframes startingat the beginning of the first available SC Period which starts at least4 subframes after the subframe in which the sidelink grant was received,overwriting a previously configured sidelink grant occurring in the sameSC period, if available, and clear the configured sidelink grant at theend of the corresponding SC Period.

If the MAC entity has a configured sidelink grant occurring in thissubframe, and if the configured sidelink grant corresponds totransmission of SCI, the MAC entity shall, for each subframe, instructthe physical layer to transmit SCI corresponding to the configuredsidelink grant.

If the MAC entity has a configured sidelink grant occurring in thissubframe, and if the configured sidelink grant corresponds totransmission of first transport block, the MAC entity shall deliver theconfigured sidelink grant and the associated HARQ information to theSidelink HARQ Entity for this subframe.

For PDU(s) associated with one SCI, MAC shall consider only logicalchannels with same Source Layer-2 ID-Destination Layer-2 ID pairs.

In ProSe communication, the UE must have a SL grant for SL datatransmission. In Rel-12, the SL grant has following characteristics:within one SC period, SL data of only one ProSe Group can betransmitted, and for one ProSe Group (r destination), only one SL grantis used.

In summary, within one SC period, a ProSe UE transmits SL data of onlyone ProSe destination by using only one SL grant.

If the UE receives multiple SL grants for an SC period, the UEoverwrites the previous ones, if any, and uses the only the lastreceived SL grant.

When the UE receives an SL grant, as there is no indication in SL grantwith which group the SL grant is associated, the UE by itself selectsone ProSe destination and generates a MAC PDU by including only the SLdata of the selected ProSe destination.

In Rel-13, ProSe Relay is introduced in LTE. For ProSe Relay, an eNBforwards SL data of Remote UE to a Relay UE, and the Relay UE forwardsSL data to the Remote UE. As the Relay UE is likely to serve as a relayfor multiple Remote UEs, the Relay UE will receive SL data of multipleRemote UEs from the eNB. Accordingly, the Relay UE is different from aRel-12 ProSe UE in that the Relay UE may need to transmit SL data tomultiple Remote UEs within one SC period.

For this, 1) the eNB needs to provide multiple SL grants to the Relay UEwherein each SL grant should be associated with one specific ProSedestination (one Remote UE), and 2) the UE can transmit SL data ofmultiple ProSe destinations within one SC period.

FIG. 12 is a diagram for transmitting a sidelink data in a D2Dcommunication system according to embodiments of the present invention.

It is invented that a Relay UE receives at least one SL grant via MACsignal from an eNB, wherein each SL grant is to be used for SL datatransmission of one ProSe destination.

The ProSe Group refers a ProSe Destination indicating a destination(s)for relay or non-relay related one-to-one or one-to-many sidelinkcommunication. For one-to-one communication, the destination isidentified by the Layer-2 ID for unicast communication, while forone-to-many communication, the destination is identified by the ProSeLayer-2 Group ID.

An eNB is transmitting SL data to a Remote UE via a Relay UE, whereinthe Relay UE is to serve at least one Remote UE.

The SL data comprises two types of data. If the SL data is data to berelayed from the eNB to the Remote UE via the Relay UE, the SL datarefers a relay data, or if the SL data is data generated by the UE, theSL data refers a ProSe data. In this invention, the SL data refers therelay data.

The Relay UE is configured to communicate with at least one ProSedestination (S1201).

Preferably, the Relay UE and the Remote UE belong to one ProSedestination, wherein the Relay UE belongs to at least one ProSedestination.

If the eNB has SL data available for transmission for a ProSedestination to which the Remote UE belongs, the eNB transmits the SLdata corresponding to a ProSe destination of the at least one ProSedestination to a UE (S1203).

The eNB generates a SL grant MAC CE including the SL grant for the ProSedestination and/or the ProSe destination identifier of the ProSedestination with which the SL grant is associated, and transmits the SLgrant MAC CE to the Relay UE (S1205).

Preferably, the SL grant MAC CE is identified by a LCID of thecorresponding MAC subheader, and the SL grant MAC CE is a variable sizeof MAC control element.

Preferably, the ProSe destination identifier can be a Remote UEidentifier if one-to-one communication.

Preferably, the eNB can transmit the generated SL grant MAC CE and theSL data for the ProSe destination of which the SL grant is contained inthe generated SL grant MAC CE in a same MAC PDU.

When a Relay UE receives a MAC PDU from the eNB, if the received MAC PDUcontains SL data, the Relay UE stores the SL data for at least one ProSeGroup contained in the received MAC PDU. If the received MAC PDUcontains the SL grant MAC CE, the Relay UE stores the SL grantscontained in the received MAC PDU. The Relay UE considers that each SLgrant is for the ProSe Group as indicated by the corresponding ProSeGroup identifier.

Through the steps of S1203 to S1205, if the Relay UE has a SL data for aProSe destination, and the Relay UE has the SL grant associated withthat ProSe destination, the Relay UE transmits the SL data to the ProSedestination by using a SL grant associated with the ProSe destination inthe SL grant MAC CE (S1207). And the Relay UE may not trigger SL BSR.

If the Relay UE does not have the SL grant associated with that ProSedestination, the Relay UE triggers SL BSR. The Relay UE can trigger SLBSR if the SL grant for that ProSe destination is not received from theeNB for a certain time period after the Relay UE receives SL data forthat ProSe Group from the eNB.

FIGS. 13A and 13B are examples for the SL grant MAC CE according toembodiments of the present invention.

If the eNB has SL data available for transmission for multiple ProSedestinations, the eNB generates a SL grant MAC CE containing multiple SLgrants and multiple ProSe destination identifiers, wherein each ProSedestination identifier indicates the ProSe destination with which eachSL grant is associated; or the eNB generates multiple SL grant MAC CEs,wherein each SL grant MAC CE contains the SL grant and the correspondingProSe Group identifier.

FIG. 13A shows an example 1 of SL grant MAC CE according to embodimentsof the present invention. In the SL grant MAC CE, for one ProSedestination, ProSe destination identifier and the SL grant are included.And then, for another ProSe destination, ProSe destination identifierand the SL grant are included. If the sidelink grant MAC CE contains Nnumbers of sidelink grants and destination identifiers, a first sidelinkgrant and a first destination identifier for the first destination isincluded first, and a Nth sidelink grant and a Nth destinationidentifier for the Nth destination is included in a Nth, in the sidelinkgrant MAC CE.

FIG. 13B shows an example 2 of SL grant MAC CE according to embodimentsof the present invention. In the SL grant MAC CE, ProSe destinationidentifiers are included first. And then, SL grants are included in theorder of ProSe destination identifiers included before the SL grants. Ifthe sidelink grant MAC CE contains N numbers of sidelink grants anddestination identifiers, the N numbers of destination identifiers areincluded first, and the N numbers of sidelink grants are included in anorder of destination identifiers included before the N numbers ofsidelink grants.

FIG. 14 is an example for transmitting a sidelink data in a D2Dcommunication system according to embodiments of the present invention.

A Remote UE and a Relay UE belong to a ProSe Group 3 (S1401).

An eNB has SL data becomes available for transmission for ProSe Group 3,i.e., to be transmitted to the Remote UE via the Relay UE (S1403).

The eNB selects SL grant for SL data transmission of ProSe Group 3(S1405).

The eNB generates an SL grant MAC CE including, ProSe Group ID 3 and SLgrant for ProSe Group 3 (S1407).

The eNB generates a MAC PDU including the generated SL grant MAC CE andSL data for ProSe Group 3 (S1409).

The eNB transmits the generated MAC PDU to the Relay UE of ProSe Group 3(S1411).

The Relay UE stores the SL data and the SL grant for ProSe Group 3according to the ProSe Group identifier (S1413).

The Relay UE transmits the SL data to the Remote UE of ProSe Group 3 byusing the stored SL grant for ProSe Group 3 (S1415). And the Relay UEdoesn't trigger SL BSR.

The embodiments of the present invention described herein below arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

In the embodiments of the present invention, a specific operationdescribed as performed by the BS may be performed by an upper node ofthe BS. Namely, it is apparent that, in a network comprised of aplurality of network nodes including a BS, various operations performedfor communication with an MS may be performed by the BS, or networknodes other than the BS. The term ‘eNB’ may be replaced with the term‘fixed station’, ‘Node B’, ‘Base Station (BS)’, ‘access point’, etc.

The above-described embodiments may be implemented by various means, forexample, by hardware, firmware, software, or a combination thereof.

In a hardware configuration, the method according to the embodiments ofthe present invention may be implemented by one or more ApplicationSpecific Integrated Circuits (ASICs), Digital Signal Processors (DSPs),Digital Signal Processing Devices (DSPDs), Programmable Logic Devices(PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers,microcontrollers, or microprocessors.

In a firmware or software configuration, the method according to theembodiments of the present invention may be implemented in the form ofmodules, procedures, functions, etc. performing the above-describedfunctions or operations. Software code may be stored in a memory unitand executed by a processor. The memory unit may be located at theinterior or exterior of the processor and may transmit and receive datato and from the processor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

INDUSTRIAL APPLICABILITY

While the above-described method has been described centering on anexample applied to the 3GPP LTE system, the present invention isapplicable to a variety of wireless communication systems in addition tothe 3GPP LTE system.

1. A method for a user equipment (UE) operating in a wirelesscommunication system, the method comprising: configuring to communicatewith at least one destination; receiving a sidelink data correspondingto a destination of the at least one destination from an eNB; receivinga sidelink grant Medium Access Control (MAC) Control Element (CE)including at least one sidelink grant and at least one destinationidentifier associated with a corresponding sidelink grant from the eNB;and transmitting the sidelink data to the destination by using asidelink grant associated with the destination in the sidelink grant MACCE if there is the sidelink grant associated with the destination in thesidelink grant MAC CE.
 2. The method according to claim 1, wherein thedestination identifier is an identifier of group or an identifier of aUE.
 3. The method according to claim 1, wherein the sidelink grant MACCE is identified by a LCID of a corresponding MAC subheader.
 4. Themethod according to claim 1, wherein the sidelink grant MAC CE is avariable size of MAC control element.
 5. The method according to claim1, wherein the sidelink data is a data to be relayed from the eNB to thesecond UE via the UE.
 6. The method according to claim 1, wherein if thesidelink grant MAC CE contains N numbers of sidelink grants anddestination identifiers, a first sidelink grant and a first destinationidentifier for the first destination is included first, and a Nthsidelink grant and a Nth destination identifier for the Nth destinationis included in a Nth, in the sidelink grant MAC CE, or the N numbers ofdestination identifiers are included first, and the N numbers ofsidelink grants are included in an order of destination identifiersincluded before the N numbers of sidelink grants.
 7. The methodaccording to claim 1, wherein the UE doesn't trigger sidelink BSR forthe sidelink data for the destination.
 8. The method according to claim7, wherein if the sidelink data of the sidelink logical channel isreceived from the eNB, the UE triggers the BSR when a certain time ispassed after the sidelink data of the sidelink logical channel isreceived from the eNB.
 9. A user equipment (UE) operating in a wirelesscommunication system, the UE comprising: a Radio Frequency (RF) module;and a processor operably coupled with the RF module and configured to:configuring to communicate with at least one destination; receive asidelink data corresponding to a destination of the at least onedestination from an eNB; receive a sidelink grant Medium Access Control(MAC) Control Element (CE) including at least one sidelink grant and atleast one destination identifier associated with a correspondingsidelink grant from the eNB; and transmit the sidelink data to thedestination by using a sidelink grant associated with the destination inthe sidelink grant MAC CE if there is the sidelink grant associated withthe destination in the sidelink grant MAC CE.
 10. The UE according toclaim 9, wherein the destination identifier is an identifier of group oran identifier of a UE.
 11. The UE according to claim 9, wherein thesidelink grant MAC CE is identified by a LCID of a corresponding MACsubheader.
 12. The UE according to claim 9, wherein the sidelink grantMAC CE is a variable size of MAC control element.
 13. The UE accordingto claim 9, wherein the sidelink data is a data to be relayed from theeNB to the second UE via the UE.
 14. The UE according to claim 9,wherein if the sidelink grant MAC CE contains N numbers of sidelinkgrants and destination identifiers, a first sidelink grant and a firstdestination identifier for the first destination is included first, anda Nth sidelink grant and a Nth destination identifier for the Nthdestination is included in a Nth, in the sidelink grant MAC CE, or the Nnumbers of destination identifiers are included first, and the N numbersof sidelink grants are included in an order of destination identifiersincluded before the N numbers of sidelink grants.
 15. The UE accordingto claim 9, wherein the UE doesn't trigger sidelink BSR for the sidelinkdata for the destination.
 16. The UE according to claim 15, wherein ifthe sidelink data of the sidelink logical channel is received from theeNB, the UE triggers the BSR when a certain time is passed after thesidelink data of the sidelink logical channel is received from the eNB.